ISDN based communication systems are quickly becoming the standard for voice and data communication systems given their ability to combine standard telephone or voice type communications which typically is performed by circuit switches which occupy an entire communication path, with the advantages of data communication systems which often transmit data in packets. As a rule, existing data or packet communication technology and pure telephone technology can generally not be applied to solving ISDN based communication problems.
There are currently two ISDN based communication services or interface methods. The first, illustrated in FIG. 1, is the conventional primary rate interface (PRI) method which is used in a point-to-point configuration typically connecting first and second Data Termination Equipment (DTE) such as central offices over first and second trunk lines.
In a second service type system, commonly referred to as basic rate interface (BRI), the current CCITT standard of ISDN allows a point-to-two-point communication topography as illustrated in FIGS. 2 and 3. The interface specification for this ISDN standard is expressly limited to two DTE connected to a central office, other DTE, or other centrally located telephony control unit.
None of the current ISDN interface standards support service to more than two points from a central unit. Given the popularity and proliferation of ISDN service, however, it is preferred and indeed desirable that present and future communication systems follow ISDN service guidelines. Given the increased usage of ISDN based communication services and the cost of providing central DTE's such as telephony units, it is now apparent that new systems must be designed which allow a central DTE such as a telephony type unit to support communication to a large number of telephony modules. Presently, the ISDN standard interfaces do not support such a configuration.
Several prior art systems exist which attempt to overcome the limitations of the ISDN interfaces, as presently defined, in the hopes of providing such point-to-multipoint communication service. For example, U.S. Pat. No. 5,187,707 to Chu, et al. as well as other equivalent systems all utilize a multiplexing scheme whereby a number of terminal communication equipment are time multiplexed over one communication channel. Such a system results in a fixed or predetermined time slot for each terminal communication equipment. In all of the systems, the system topography is a multiple drop bus configuration. Most importantly, none of the prior art allows such an ISDN system to maintain the state of each terminal communication equipment. Finally, none of the prior art systems allow the communication equipment to be automatically configurable, thereby allowing the system to quickly and easily establish an equipment availability and identification map.
Accordingly, what is required is an communication system and method for providing point-to-multipoint communication services utilizing a currently defined and established protocol such as ISDN. Additionally, such a system must be able to be automatically mapped into a central data terminal equipment unit so as to establish a table of currently connected and available communication equipment, each of which should be uniquely and individually addressable without the need for multiplexing.